The present invention relates to a dual purpose hand cart convertible between a two wheel, upright, or vertical loading hand cart and a four wheel, horizontal loading hand cart with improved means for locking the two wheels for the four wheel configuration to the two wheel structure.
Home Improvement stores carry a variety of items that range in size from simple hardware items to very large items such as lumber or similar bulky goods that require wheeled material transport devices for customers to transport their purchased goods to their motor vehicles or trucks. The two wheeled hand carts are used for transporting small packages that can be vertically stacked on to a two wheel hand cart. Builder""s supplies, for example, generally require a wheeled transport device that are beyond the load capacity of a two wheel, hand cart. The dual purpose hand cart that is convertible between a two wheel, upright hand cart and a four wheel, horizontal load supporting platform for stacking bulky items such as lumber or the like has been found suitable for use in these home improvement stores or outlets.
These dual purpose hand carts are well known in the art and are exemplified, for example, by the disclosure in U.S. Pat. No. 3,785,669 for a convertible bulk hand cart. This patent disclosure describes a manually operated, wheeled material handling cart which is convertible between a two wheel hand cart of conventional configuration and a four wheel hand cart having a horizontal load carrying platform for stacking cases of bottled liquids or the like. This prior art device further utilizes a rudimentary locking means for locking the two wheel supporting structure used in the four wheel configuration, to the two wheel configuration yet enables the usual ease of use for the two wheel hand cart without the need for supplying separate material handling devices or specially designed material handling carts for specific purposes.
In all known prior art dual purpose devices of this type the locking devices are generally spring loaded and released to permit the conversion between the two wheel configuration to the four wheel configuration. The patented locking device of the aforementioned U.S. Pat. No. 3,785,669 utilizes a plurality of locking elements that are controlled to rotate between a position locking a latching bar and freeing the bar and thereby permit the user to unfold the wheeled structure to convert the hand cart to the four wheel construction or the platform cart. The experience with such locking mechanism is that it readily wears and as a result renders the latch or locking mechanism loose, effectively reducing its useful life. Accordingly, there is a present need for an improved locking mechanism with a more positive locking action and longer useful life.
The present invention provides an improved dual purpose hand cart capable of use as two wheel, upright hand cart and a four wheel, horizontal hand cart with improved means for locking the structure required for conversion to a four wheel cart having a more positive latch or locking function, with less parts required and longer useful life. The locking mechanism is based on the sliding action of the latching rod and associated locking elements rather than any rotary action. The release of the locking mechanism is designed for xe2x80x9chands freexe2x80x9d operation when a foot release is operated.
From a broad method standpoint, the improved locking concept for use with a dual purpose hand cart includes the step of
providing a two wheel hand cart having spaced, longitudinally extending side rails for pivotably securing a second pair of longitudinally extending side rails arranged in a spaced, parallel relationship with the side rails for the two wheel hand cart. The second pair of side rails includes a brace rod extending between said second pair of side rails and movable therewith. The method further contemplates providing locking means for securement to the side rails for the two wheel hand cart and securing the locking means to the side rails to permit the locking means to slide in a substantially vertical plane for locking and unlocking purposes in response to corresponding forces applied thereto and normally arranged in a locking position. In order to lock up the brace rod, imparting a swinging movement to the second pair of side rails causing the brace rod to impact the locking means to cause the locking means to be momentarily, slidably moved out of its locking position so that the brace rod assumes the locking position and then the locking means automatically moves back to the locking position for locking up the brace rod. The aforementioned method further contemplates providing manual release means, operable hands free, arranged with the locking means for causing the locking means to slide away from its locking position with the brace rod to permit the commencement of the conversion to the four wheel hand cart upon the application of releasing force to the release means.
From a structural standpoint, the present invention contemplates a dual purpose hand cart comprising a two wheel hand cart characterized as including a pair of spaced, longitudinally extending side rails and a second pair of spaced, longitudinally extending side rails carrying wheel means individual to each of the side rails and a brace rod extending between the side rails. Pivot means secures the second pair of side rails to the side rails for the two wheel cart so that the second pair of rails assumes a spaced, substantially parallel relationship with the side rails for the two wheel cart and is swingable away from the parallel relationship to permit the wheels for the second pair of side rails to engage a supporting surface. Locking means are secured to the side rails for the two wheel hand cart for locking up and unlocking the brace rod to cause the second pair of side rails to be locked in the parallel relationship with the side rails for the two wheel cart. The locking means includes a latch rod mounted to the side rails for sliding movement in a substantially vertical plane along with locking means arranged adjacent each end and constructed and defined for receiving the brace rod and locking up the rod in a releasable arrangement. Yieldable means in the form of a spring or the like is secured between an individual side rail and an individual locking means for normally positioning each of the locking means into a locking position and yieldable therefrom upon the engagement of the brace rod therewith with sufficient force to cause the movement of the locking means in a direction to allow the brace rod to be positioned in a locking position and to be locked up. A foot operable release means are pivotably mounted to the side rails for the two wheel cart for receiving a releasing force to cause the sliding movement of the latch rod and the locking means away from its locking position thereby permitting the second pair of side rails to be pivoted outside of the locking means for commencing the conversion of the two wheel hand cart when the release means is actuated by the users foot and his hands are free to swing the second pair of side rails outwardly of the locking means.